Engine Controls/fuel - 4.8l (l20), 5.3l (Lmf), or 6.0l (l96 lc8) - Description and Operation

Engine Control Module Description

The Engine Control Module (ECM) interacts with many emission related components and systems, and monitors emission related components and systems for deterioration. OBD II diagnostics monitor the system performance and a diagnostic trouble code (DTC) sets if the system performance degrades. The ECM is part of a network and communicates with various other vehicle control modules.

Malfunction indicator lamp (MIL) operation and DTC storage are dictated by the DTC type. A DTC is ranked as a Type A or Type B if the DTC is emissions related. Type C is a non-emissions related DTC.

The ECM is the control center of the engine controls system. Review the components and wiring diagrams in order to determine which systems are controlled by the ECM.

The ECM constantly monitors the information from various sensors and other inputs, and controls the systems that affect engine performance and emissions. The ECM also performs diagnostic tests on various parts of the system and can turn on the MIL when it recognizes an operational problem that affects emissions. When the ECM detects a malfunction, the ECM stores a DTC. The condition area is identified by the particular DTC that is set. This aids the technician in making repairs.

ECM Function

The ECM can supply 5 V or 12 V to various sensors or switches. This is done through pull-up resistors to regulated power supplies within the ECM. In some cases, even an ordinary shop voltmeter will not give an accurate reading due to low input resistance. Therefore, a digital multimeter (DMM) with at least 10 megaohms input impedance is required in order to ensure accurate voltage readings.

The ECM controls the output circuits by controlling the ground or the power feed circuit through transistors or a device called an output driver module.

EEPROM

The electronically erasable programmable read only memory (EEPROM) is an integral part of the ECM. The EEPROM contains program and calibration information that the ECM needs in order to control engine operation.

Special equipment, as well as the correct program and calibration for the vehicle, are required in order to reprogram the ECM.

Data Link Connector (DLC)

The data link connector (DLC) provides serial data communication for ECM diagnosis. This connector allows the technician to use a scan tool in order to monitor various serial data parameters, and display DTC information. The DLC is located inside the driver's compartment, underneath the instrument panel.

Malfunction Indicator Lamp (MIL)

The malfunction indicator lamp (MIL) is inside the instrument panel cluster (IPC). The MIL is controlled by the ECM and illuminates when the ECM detects a condition that affects vehicle emissions.

ECM Service Precautions

The ECM, by design, can withstand normal current draws that are associated with vehicle operations. However, care must be used in order to avoid overloading any of these circuits. When testing for opens or shorts, do not ground or apply voltage to any of the ECM circuits unless the diagnostic procedure instructs you to do so. These circuits should only be tested with a DMM unless the diagnostic procedure instructs otherwise.

Emissions Diagnosis For State I/M Programs

This OBD II equipped vehicle is designed to diagnose any conditions that could lead to excessive levels of the following emissions

Hydrocarbons (HC)
Carbon monoxide (CO)
Oxides of nitrogen (NOx)
Evaporative emission (EVAP) system losses

Should this vehicle's on-board diagnostic system (ECM) detect a condition that could result in excessive emissions, the ECM turns ON the MIL and stores a DTC that is associated with the condition.

Aftermarket (Add-On) Electrical And Vacuum Equipment

CAUTION

Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle components or systems.

CAUTION

Connect any add-on electrically operated equipment to the vehicle's electrical system at the 12 V battery (power and ground) in order to prevent damage to the vehicle.

Aftermarket, add-on, electrical and vacuum equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the vehicle's electrical or vacuum systems. No allowances have been made in the vehicle design for this type of equipment.

Add-on electrical equipment, even when installed to these strict guidelines, may still cause the powertrain system to malfunction. This may also include equipment not connected to the vehicle electrical system, such as portable telephones and radios. Therefore, the first step in diagnosing any powertrain condition is to eliminate all of the aftermarket electrical equipment from the vehicle. After this is done, if the problem still exists, the problem may be diagnosed in the normal manner.

Electrostatic Discharge (ESD) Damage

Note. In order to prevent possible electrostatic discharge damage to the ECM, DO NOT touch the connector pins on the ECM.

The electronic components that are used in the control systems are often designed to carry very low voltage. These electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 V of static electricity can cause damage to some electronic components. By comparison, it takes as much as 4,000 V for a person to even feel a static discharge.

There are several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of charging by friction is a person sliding across a car seat.

Charging by induction occurs when a person with well insulated shoes stands near a highly charged object and momentarily touches ground. Charges of the same polarity are drained off leaving the person highly charged with the opposite polarity. Static charges can cause damage, therefore, it is important to use care when handling and testing electronic components.

Emissions Control Information Label

The underhood Vehicle Emissions Control Information Label contains important emission specifications. This identifies the year, the displacement of the engine in liters, and the class of the vehicle.

This label is located in the engine compartment of every General Motors vehicle. If the label has been removed, it can be ordered from GM service parts operations (GMSPO).

Scheme 197

Scheme 197: Throttle Actuator Control (TAC) System Description

The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the driver's intent based on input from the accelerator pedal position sensors, then calculates the appropriate throttle response based on the throttle position sensors. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the throttle actuator motor. The throttle blade is spring loaded in both directions, and the default position is slightly open.

Modes Of Operation

Normal Mode

During the operation of the TAC system, several modes, or functions, are considered normal. The following modes may be entered during normal operations

Minimum pedal value-At key-up, the ECM updates the learned minimum pedal value.
Minimum throttle position values-At key-up, the ECM updates the learned minimum throttle position value. In order to learn the minimum throttle position value, the throttle blade is moved to the Closed position.
Ice break mode-If the throttle blade is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
Minimum pedal value-At key-up, the ECM updates the learned minimum pedal value.
Battery saver mode-After a predetermined time without engine RPM, the ECM commands the Battery Saver mode. During the Battery Saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.

Reduced Engine Power Mode

When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions

Acceleration limiting-The ECM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.
Limited throttle mode-The ECM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.
Throttle default mode-The ECM will turn OFF the throttle actuator motor, and the throttle will return to the spring loaded default position.
Forced idle mode-The ECM will perform the following actions: Limit engine speed to idle positioning the throttle position, or by controlling the fuel and spark if the throttle is turned OFF. Ignore the accelerator pedal input.
Engine shutdown mode-The ECM will disable fuel and de-energize the throttle actuator.

Camshaft Position (CMP) Actuator System

The camshaft (CMP) actuator system is an electro-hydraulic operated device used for a variety of engine performance and operational enhancements. These enhancements include lower emission output through exhaust gas dilution of the intake charge in the combustion chamber, a broader engine torque range, and improved fuel economy. The CMP actuator system accomplishes this by, changing the angle or timing of the camshaft, relative to the crankshaft position. The CMP actuator simply allows earlier or later intake and exhaust valve opening, during the four stroke engine cycle. The CMP actuator cannot vary the duration of valve opening, or the valve lift.

During engine OFF, engine idling conditions, and engine shutdown, the camshaft actuator is held in the park position. Internal to the CMP actuator assembly is a return spring and a locking pin. During non-phasing modes of the camshaft, the return spring rotates the camshaft back to the park position, and the locking pin retains the CMP actuator sprocket to the camshaft. The engine control module (ECM) can only command the CMP actuator to retard the valve timing from the park position, or advance the valve timing back to the park position.

CMP Actuator System Operation

The camshaft position (CMP) actuator system is controlled by the engine control module (ECM). The ECM sends a pulse width modulated, signal to the CMP actuator solenoid to control the amount of pressurized engine oil, into the CMP actuator. A low reference circuit, or ground wire between the CMP actuator solenoid and the ECM completes the electrical circuit. To regulate the pressurized engine oil into the CMP actuator, the solenoid uses electromagnetic force on the solenoid pintle to pulse the oil control spool valve. The pressurized engine oil is sent to unseat the locking pin, and to the vane and rotor assembly of the CMP actuator, to either retard or advance the valve timing. The ECM will control the amount of ON time applied to the solenoid, through the signal from the ECM.

The ECM uses the following inputs before assuming control of the CMP actuator, and to calculate the optimum valve timing.

Engine speed
Manifold absolute pressure (MAP)
Throttle position angle
Camshaft position sensor (CMP)
Crankshaft position sensor (CKP)
Crankshaft/camshaft correlation
Engine coolant temperature (ECT)
Closed loop fuel control
Engine oil pressure (EOP)
Engine oil level
CMP actuator solenoid circuit state

Fuel System Overview

The compressed natural gas (CNG) fuel system operates similar to the gasoline version. The main differences being the storage, delivery, and safety devices within the high pressure CNG system. The engine control module (ECM) energizes the fuel pump relay that powers the CNG control module. The CNG control module supplies power and ground to the 4 high pressure lock-out solenoid valve and fuel pressure regulator. This allows CNG to flow through the high pressure lines through the fuel pressure regulator up to the fuel rail. The ECM controls the injector pulse width and timing as needed for proper engine performance.

Compressed Natural Gas (CNG) Fuel Tanks

The CNG fuel tanks are constructed of steel and conform to NGV2-1 (Type 1) specifications. A high pressure lock-off solenoid valve is threaded into the end of each fuel tank and is used to prevent fuel flow during non-operational running conditions. Metal shields are used to protect the fuel tanks from road debris or other contact conditions that may occur.

The system utilizes 4 CNG fuel tanks 2 that are mounted in tandem behind the rear axle, 1 mid-ship under the vehicle, and 1 in the cargo compartment.

Note. Federal Government Regulations require that the fuel tanks and brackets be inspected every three years or 60,000 km (36,000 m), whichever occurs first. Inspection results should be recorded in the inspection record section of the CNG owners manual supplement. The service life of a type 1 CNG fuel tank is 15 years from the date of manufacture. All CNG fuel tanks regardless of inspection results must be removed from service after this 15 year period

CNG High Pressure Lock-Off (HPL) Solenoid Valves

The HPL solenoid valve is a normally closed solenoid valve. The HPL solenoids, along with the high pressure regulator (HPR) solenoid prevents fuel flow when in the closed position. The ECM commands fuel pump relay "ON" at every ignition cycle for 4.8 seconds. This supplies power to the CNG control module to prime the fuel system and allow the fuel tank pressure (FTP) sensor to monitor the pressure for fuel gauge display. The CNG control module commands all solenoids "ON" when the fuel pump relay is energized. The ECM energizes the fuel pump relay when engine RPM indicates a crank or run condition is present.

CNG Tank Pressure Relief Device (PRD)

Note. All external PRD devices are connected directly to fuel storage pressure and cannot be isolated from the high pressure system. Do not attempt to service these devices or connect tubing/hoses unless you are absolutely certain that the system is completely empty of CNG fuel.

Each HPL solenoid valve contains an integral thermally-activated Pressure Relief Device (PRD). The PRD will activate when exposed to temperatures of approximately 108°C (220°F). In addition, there are three externally mounted PRD devices, two are equipped with a thermally and pressure-activated PRD and one is a thermally-activated PRD only. The pressure activated PRD function provides additional protection and activates when CNG tank pressure becomes too high for safe operation (approximately 37,231 kPa (5400 psig).

The combination Temperature and Pressure devices are located as follows

One between the aft axle CNG tanks
One at the mid-ship (between axles) CNG tank

The external thermal only device PRD is located at the opposite-end of the HPL solenoid valve of the mid-ship tank.

CNG Fill Receptacle and Lines

Note. Before refueling, the O-ring must be inspected and replaced if missing or damaged. The vehicle is shipped with three replacement O-rings placed in the glove compartment. Replacement O-rings are available through the GM parts network.

The CNG fill receptacle is a NGV1 profile and mates to any NGV1 fill dispenser valve. The fill dispenser seals to the receptacle with an O-ring. The fill receptacle is mounted in the vehicle fill pocket behind the fuel access door. Refer to the CNG owners manual supplement for refuel procedures.

The fuel fill line is a combination of flex hose and tubing. All connections are sealed by O-rings. The fill line runs from the receptacle to the check valve. The check valve is intended to minimize the amount of fuel leakage in the event the receptacle develops a leak.

CNG Fuel Lines

The CNG fuel system utilizes different fuel line types depending upon the working pressure and vehicle interface requirement the fuel line is required to handle.

Note. O-rings must be replaced with the correct replacement part when inspection reveals damage, etc. Hose, lines, and fittings must be replaced with approved GM service part

High Pressure Line and Hose

The high pressure line is a combination of stainless steel tubing and stainless steel jacketed PTFE hose that are certified to NGV 3.1. All connections between lines and components are of the O-ring Face Seal (ORFS) design and are sealed by specific O-rings manufactured specifically for CNG operation.

Low Pressure Line and Hose

The low pressure line is a combination of stainless steel tubing and stainless steel jacketed PTFE hose that are certified to NGV 3.1. All connections between lines and components are of the O-ring Face Seal (ORFS) design and are sealed by specific O-rings manufactured specifically for CNG operation.

CNG 1/4 Turn Isolation Valve

The high pressure fuel system is equipped with a manually-operated isolation valve located forward of the rear wheels on the left side of the vehicle at the top inboard side of the LH frame rail. A label applied to the lower body panel indicates the approximate location of this valve. The purpose of the valve is to isolate the high pressure side of the fuel system for some service procedures. If this valve is inadvertently left in the "OFF" position, the vehicle will not be operable. Refer to the CNG owners manual supplement for operating instructions.

Fuel Tank Pressure (FTP) Sensor

The fuel tank pressure (FTP) sensor is a pressure transducer. The CNG control module supplies a 5.0 V reference signal to the transducer. The transducer output varies from approximately 4.5 V when system is full to 0.5 V when the system is empty. The CNG control module provides a signal to the ECM to that will indicate the CNG system fuel level.

Note. When refueling in cold ambient conditions, the fuel gauge may not display "FULL" even though the temperature-compensated refueling event produces a temperature-compensated "FULL" condition. This is due to commercial refueling station output regulated by a temperature vs. pressure strategy to prevent the vehicle from becoming over-pressurized if relocated to a warmer ambient location after refueling.

CNG Fuel Filter

The CNG fuel filter is a high pressure coalescing media filter located forward of the CNG 1/4 turn Isolation Valve. This filter requires periodic service intervals which can be found in the CNG owners manual supplement or the service manual.

Compressed Natural Gas (CNG) Control Module

The CNG control module provides two functions when energized.

Provides a 5 V reference voltage to the FTP sensor and converts the value to a signal that it supplies to the ECM for proper fuel level display.
Provides power and ground to the high pressure lock-out (HPL) solenoid valve and high pressure regulator (HPR) solenoid when the fuel pump relay is energized.

High Pressure Regulator (HPR)

The high pressure regulator (HPR) is supplied with fuel by the fuel supply system at pressures up to 24821 kPa (3600 psig) at 21°C (70° F). Fuel flow begins when the ignition is cycled and the HPL and HPR solenoids energized. The outlet pressure is regulated to 7 - 8 bar (90 - 110 psig) and delivered through the low pressure lines to the fuel rail and CNG injectors. The HPR is connected to the engine cooling system by an inlet and outlet circuit which intercepts the heater hoses between the engine and heater core to prevent icing. The HPR also has an integral pressure burst disc (PRD) which will rupture if outlet pressure exceeds 1896 kPa (275 psig). The solenoid assembly and ORFS O-rings are the only serviceable components of the HPR.

CNG Fuel Injectors

The CNG Fuel Injectors are specific to Gaseous Fuel use. The operation of these injectors is controlled by the ECM. The injectors are installed in the base vehicle fuel rail and require spacers between the injector and manifold injector boss for proper installation. The injectors are sealed with O-rings in an identical manner to the gasoline version

On-Board Refueling Vapor Recovery System (ORVR)

The On-Board Refueling Vapor Recovery System (ORVR) is an on-board vehicle system designed to recover fuel vapors during the vehicle refueling operation. ON CNG vehicles this system is not functional although the purge solenoid is still required for proper vehicle operation.

Scheme 198

Scheme 198: Fuel Rail Assembly

The fuel rail assembly attaches to the engine intake manifold. The fuel rail assembly performs the following functions

Positions the injectors (3) in the intake manifold
Distributes fuel evenly to the injectors

Fuel Metering Modes of Operation

The engine control module (ECM) monitors voltages from several sensors in order to determine how much fuel to give the engine. The ECM controls the amount of fuel delivered to the engine by changing the fuel injector pulse width. The fuel is delivered under one of several modes.

Starting Mode

When the ignition is first turned ON, the ECM supplies voltage to the CNG control module for 4.8 seconds. While this voltage is being received, the CNG control module provides power and ground to the HPL and HPR solenoid valves. The ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode

If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the engine. When the TP sensor is at wide open throttle (WOT), the ECM reduces the fuel injector pulse width in order to increase the air to fuel ratio. The ECM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the ECM returns to the starting mode.

Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The ECM ignores the signal from the heated oxygen sensors (HO2S). The ECM calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions

Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the ECM calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode

When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly. To prevent possible hesitation, the ECM increases the pulse width to the injectors to provide extra fuel during acceleration. This is also known as power enrichment. The ECM determines the amount of fuel required based upon the TP, the ECT, the MAP, the MAF, and the engine speed.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The ECM monitors the corresponding changes in the TP, the MAP, and the MAF. The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters.

Battery Voltage Correction Mode

When the battery voltage is low, the ECM compensates for the weak spark delivered by the ignition system in the following ways

Increasing the amount of fuel delivered
Increasing the idle RPM
Increasing the ignition dwell time

Fuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability

The ignition is OFF. This prevents engine run-on.
The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
The engine speed is too high, above red line.
The vehicle speed is too high, above rated tire speed.
During an extended, high speed, closed throttle coast down-This reduces emissions and increases engine braking.
During extended deceleration, in order to prevent damage to the catalytic converters

Fuel Trim

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage while in Closed Loop and regulates the fuel delivery by adjusting the pulse width of the fuel injectors based on this signal. The ideal fuel trim values are around 0 percent for both short term and long term fuel trim. A positive fuel trim value indicates the ECM is adding fuel in order to compensate for a lean condition by increasing the pulse width. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition by decreasing the pulse width. A change made to the fuel delivery changes the short term and long term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltage. These changes fine tune the engine fueling. The long term fuel trim makes coarse adjustments to the fueling in order to re-center and restore control to short term fuel trim. A scan tool can be used to monitor the short term and long term fuel trim values. The long term fuel trim diagnostic is based on an average of several of the long term speed load learn cells. The ECM selects the cells based on the engine speed and engine load. If the ECM detects an excessive lean or rich condition, the ECM will set a fuel trim diagnostic trouble code (DTC).

The LPEFI® system is a 4 tank system, 3 secondary tanks at the rear of the vehicle and 1 main tank near the center of the vehicle. The LPEFI® system is a direct replacement propane fuel injection system. It replaces the gasoline fuel injection system and works the same as a gasoline fuel injection system with the exception it injects propane, in a liquid state, into the intake port. The gasoline system electronic engine management stays the same and controls the LPEFI® system just as it did the gasoline injection system. Onboard diagnostics remain unchanged so the same scan tool and diagnostic approach remains equal to a gasoline system.

The LPEFI® system consists of three main components: the tank, the fuel lines and the injectors. The tanks are located to the rear and middle of the vehicle and the lines are routed forward to the engine compartment where the injector rail assemblies are mounted in the same position as the original gasoline injector rails were installed. The fuel tank is the most complicated area of the system. It includes an internal electric fuel pump & filter, fuel supply & return valves, baffle that keeps the pump submerged in liquid propane and various other valves, fuel level float assembly, pressure relief valve, overfill prevention device, liquid and vapor service valves. LPEFI® vehicles are fitted with two tanks, a main tank, which controls all fuel delivery to the injectors and an optional tank, which only transfers fuel to the main fuel tank. The main fuel tank fuel pump increases or boosts the tank pressure by 35 to 50 psi. No matter what the propane tank internal pressure is, the pump boost remains the same. This is how the propane stays a liquid throughout the liquid supply section of the system. The fuel is supplied to the injectors and whether the injector is open or not fuel passes through a cooling bushing in the injector and is returned to the tank. This is called a refrigeration cycle and also aids in maintaining the fuel in a liquid state throughout the supply passageways in the system. Because propane easily vaporizes, when the refrigeration cycle stops (when the engine is turned off) or if the return valve malfunctions closed, the propane will vaporize and cause a loss in power or hard hot restarting. To help in hot restarting, the system goes through a purge cycle for 10 to 15 seconds before every start up attempt. This strategy is built into the system's liquid propane control module. During the purge cycle the "Wait to Start" lamp will be illuminated.

Fuel Tanks

The fuel tanks meet American Society of Mechanical Engineers (ASME) design for a working pressure of 2154.6 kPa (312.5 psi) and a burst pressure of 8618 kPa (1250 psi). Baffles are built in the tank to keep the fuel pump submerged in the liquid propane. At the end of the main tank is a bulkhead that provides access to the fuel pump, fuel filter, and overfilling protection device.

Overfilling Prevention Device

The overfilling prevention device is a mechanical float-actuated valve that stops the tank from filling more than 80%. By code, you should not fill a propane vehicle tank more than 80% full of liquid, to allow room for the liquid propane to expand when it gets warm. There is also a fixed liquid level gauge. This is a small valve located at the 80 % liquid level on the tank. To fill a tank using the fixed liquid level gauge open the valve before filling. Propane vapor will hiss out. When the liquid reaches the height of this valve the liquid propane will show up as a white mist. When the mist is present stop filling the tank and close the valve.

Over Flow Valves

Every inlet of outlet valve on the liquid propane tanks has a built in over flow valve. If propane tries to exit the system at a higher rate then the calibrated amount the difference in pressure closes the over flow valve and restricts the flow. The valve closes down to a 0.080 in diameter orifice. Once the difference in pressure is equalized the over flow valve will open.

Pressure Relief Valve

If the pressure in the fuel tank exceeds 2155 kPa (312.5 psi), the pressure relief valve (PRV) will vent propane vapor to the atmosphere. The pressure will not get this high unless the tank has been overfilled, or unless the tank is hotter than 60°C (140°F). When the PRV vents, the sudden pressure drop significantly cools the remaining liquid, because the boiling of the propane absorbs heat.

Fill Filter

The fill filter is located between the fill valve and the fill hoses that go to the fuel tanks. The fill filter is a traps particles larger than 3 microns to help reduce any contamination from the filling equipment and is required to be replaced at the proper maintenance intervals.

Fill Valve

LPEFI® vehicles use a standard pro-pane vehicle refueling fitting (Sherwood 1855 series) with integral back-check valve.

Fuel Pump Filter

The fuel pump filter is mounted to the inlet of the fuel pump assembly inside the main fuel tank.

Fuel Pump

The fuel pump is mounted inside the main fuel tank and is used to increase line pressure of the liquid propane by 35-50 psi over the internal tank pressure to insure the liquid state of the propane is maintained. The inlet to the fuel pump is submerged in liquid at all times by a baffle in the tank assembly.

Fuel Transfer Pump

The liquid propane control module monitors each of the fuel level sensors. When the liquid propane control module detects a difference in fuel tank levels it supplies power to the fuel transfer pump and secondary fuel supply solenoid. The liquid propane is pumped from the secondary tanks to the main tank to ensure adequate fuel is supplied to the engine.

The main fuel tank has a scavenge pump that operates when the main fuel pump is energized. The scavenge pump ensures the baffle area of the main tank is full of liquid propane.

Fuel Lines

The fuel lines consist of two flexible hoses, one inside the other, in a concentric arrangement. The nylon inner line supplies liquid propane to the injectors while the area between the outside of the inner line and the larger outer hose is the fuel return passage. The concentric fuel line design has a number of benefits

Cuts the number of possible leak points in half
Reduces vapor-lock in the supply line by using the return fuel passage as insulation
Postpones the vapor-lock that occurs after a hot engine is shut off
Shortens the purge cycle time needed to restart a hot engine.

Fuel Level Sensors

A float and arm type fuel level sensor is used in the main and front secondary fuel tanks. The liquid propane control module monitors each sensor and provides an output to the engine control module. If the difference in fuel level between the tanks going out of the calibrated range the liquid propane control module will turn on the secondary tank fuel pump.

Liquid Propane Delivery Module

The liquid propane delivery module is mounted to the outlet end of the main fuel tank and houses the supply and return fuel solenoid valves. The fuel supply and return solenoids are 12 V electro-mechanical valves that close when not energized. The fuel supply solenoid is energized whenever the vehicle is running or in purge mode. The return solenoid is only energized during purge mode.

A secondary liquid propane delivery module is mounted on the front of the secondary tank assembly. When the liquid propane control module senses a difference in fuel level between the primary and secondary tanks power is supplied to the secondary liquid propane delivery module. This opens the secondary supply valve and powers the secondary fuel pump. Liquid propane is then pumped to the primary tank.

Liquid Propane Control Module

The liquid propane control module is mounted on the left frame rail near the main fuel tank. The liquid propane control module controls the voltage supply to the liquid propane delivery module and liquid propane fuel pump relay. When the ignition is initially energized the liquid propane control module turns on the wait to start lamp and starts the purge mode. During purge mode the primary fuel pump, fuel supply and return solenoids are energized to allow liquid propane to circulate through the entire system. This is done to evacuate all propane gas from the fuel system. The liquid propane control module determines fuel level between the two input signals from the fuel level sensors and will enable the secondary fuel pump when the difference between the main and secondary tanks are outside the calibrated range. The liquid propane control module also supplies the engine control module with a fuel level signal.

For safety, an impact switch is mounted inside the liquid propane control module. If an impact greater the 12 g's occurs the liquid propane control module will go into shutdown mode. When this occurs all valve and pumps will be disabled, sealing the system. After the fuel system has been inspected for damage the control module may be reset by disconnecting the power to the liquid propane control module for several seconds.

Fuel Injector Rails

The fuel injector rails have the same concentric design as the fuel lines. The inner line supplies liquid propane to the injectors while the area between the outside of the inner line and the larger outer rail is the fuel return passage. This concentric design helps to maintain a liquid fuel state.

Fuel Injector

Each fuel injector has a supply passage and a return passage. The fuel injector rails have the same concentric design as the fuel lines. The passage in the injector from the supply section to the return section is restricted by a cooling bushing. As liquid propane passes through the cooling bushing, a pressure reduction takes place, which causes the propane to vaporize and effectively cools the area around the supply section. This is called a refrigeration cycle and aids in maintaining the fuel in a liquid state for all driving conditions, regardless of the outside temperature. The design of the injector compensates for changes in the fuel pressure so a fuel pressure regulator is not required.

Starting Mode

When the ignition is first turned ON, the ECM supplies voltage to the liquid propane control module for 90 seconds. While this voltage is being received, the liquid propane control module provides power to the primary fuel pump, fuel supply and return solenoids to allow liquid propane to circulate through the entire system. This is done to evacuate all propane gas from the fuel system. The ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode

Run Mode

Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.

Acceleration Mode

Deceleration Mode

Battery Voltage Correction Mode

When the battery voltage is low, the ECM compensates for the weak spark delivered by the ignition system in the following ways

Increasing the amount of fuel delivered
Increasing the idle RPM
Increasing the ignition dwell time

Fuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability

The ignition is OFF. This prevents engine run-on.
The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
The engine speed is too high, above red line.
The vehicle speed is too high, above rated tire speed.
During an extended, high speed, closed throttle coast down-This reduces emissions and increases engine braking.
During extended deceleration, in order to prevent damage to the catalytic converters

The liquid propane injection system is a 3 tank system located at the rear of the vehicle. The liquid propane injection system is a direct replacement propane fuel injection system. It replaces the gasoline fuel injection system and works the same as a gasoline fuel injection system with the exception it injects propane, in a liquid state, into the intake port. The gasoline system electronic engine management stays the same and controls the LPG system just as it did the gasoline injection system. Engine control diagnostics remain unchanged so the same scan tool and diagnostic approach remains equal to a gasoline system. The LPG control module will use the Wait to Start indicator to display flash codes if a fault is present.

The liquid propane injection system consists of three main components: the tank assembly, the fuel lines and the injectors. The tanks are located to the rear of the vehicle and the lines are routed forward to the engine compartment where the injector rail assemblies are mounted in the same position as the original gasoline injector rails were installed. The fuel tank is the most complicated area of the system. It includes an internal electric fuel pump, fuel supply & bypass valves, a baffle that keeps the pump submerged in liquid propane, fuel level float assembly, pressure relief valve, overfill prevention device, liquid and vapor service valves. The LPG fuel pump increases or boosts the tank pressure by 275-414 kPa (40-60 psi). No matter what the propane tank internal pressure is, the pump boost pressure remains the same. This is how the propane stays a liquid throughout the liquid supply section of the system. The fuel is supplied to the injectors and whether the injector is open or not fuel passes through a cooling bushing in the injector and is returned to the tank. This is called a refrigeration cycle and also aids in maintaining the fuel in a liquid state throughout the supply passageways in the system. Because propane easily vaporizes, when the refrigeration cycle stops (when the engine is turned off) or if the bypass valve malfunctions closed, the propane will vaporize and cause a loss in power or hard hot restarting. To help in hot restarting, the system goes through a purge cycle for 1 to 20 seconds, depending on temperature and pressure, before every start up attempt. This strategy is built into the system's LPG control module. During the purge cycle the "Wait to Start" indicator will be illuminated.

The fuel tanks meet American Society of Mechanical Engineers (ASME) design for a working pressure of 2154.6 kPa (312.5 psi) and a burst pressure of 8618 kPa (1250 psi). Baffles are built in the tank to keep the fuel pump submerged in the liquid propane. At the front of the tank assembly is a bulkhead that provides access to the fuel pump.

The overfilling prevention device is a mechanical float-actuated valve that stops the tank from being filled more than 80%. By code, you should not fill a propane vehicle tank more than 80% full of liquid, to allow room for the liquid propane to expand when it gets warm. There is also a fixed liquid level gauge. This is a small valve located at the 80 % liquid level on the tank. To fill a tank using the fixed liquid level gauge open the valve before filling. Propane vapor will hiss out. When the liquid reaches the height of this valve the liquid propane will show up as a white mist. When the mist is present stop filling the tank and close the valve.

Every inlet or outlet valve on the liquid propane tanks has a built in over flow valve. If propane tries to exit the system at a higher rate then the calibrated amount the difference in pressure closes the over flow valve and restricts the flow. The valve closes down to a 2 mm (0.080 in) diameter orifice. Once the difference in pressure is equalized the over flow valve will open.

The fill filter is located on the frame rail between the fuel tank and the fill valve. The fill filter traps particles larger than 3 microns to help reduce any contamination from the filling equipment and is required to be replaced at the proper maintenance intervals.

Clean Fuel vehicles use a standard pro-pane vehicle refueling fitting (Sherwood 1855 series) with integral back-check valve.

Fuel Filter

The fuel filter at the fuel pump a sock type filter is mounted to the inlet of the fuel pump assembly inside the main fuel tank. There is also a fuel filter mounted to the frame rail in the fuel supply line between the fuel tank and fuel injector rail. The frame mounted fuel filter is required to be replaced at the proper maintenance intervals.

The LPG fuel pump is mounted inside the fuel tank and is used to increase line pressure of the liquid propane by 275-414 kPa (40-60 psi) over the internal tank pressure to insure the liquid state of the propane is maintained. The inlet to the LPG fuel pump is submerged in liquid at all times by a baffle in the tank assembly.

The fuel lines are Type III LPG approved hoses with minimum permeability in order to pass evaporative shed testing. The hoses are rubber coated stainless steel braided to protect against chaffing and have a burst pressure rating of 12,066 kPa (1,750 psi).

Fuel Level Sensor

A float and arm type fuel level sensor is used in the fuel tank. As the level of fuel increases in the tank the float arm raises reducing the resistance across the sensor.

LPG Cut-Off Solenoid

The LPG cut-off solenoid valve is mounted to the outlet port of the fuel tank. The normally closed valve opens when the fuel pump relay is energized. The LPG cut-off solenoid valve has a built in over flow valve that will reduce the flow of LPG if the pressure difference between the inlet and outlet of the valve is greater than the calibrated amount. There is also a manual shut-off valve integrated into the LPG cut-off solenoid.

LPG Bypass Solenoid

The LPG bypass solenoid is mounted to the return port of the fuel tank. The normally closed valve opens when the LPG control module energizes the LPG bypass relay. When energized, fuel bypasses the fuel pressure regulator and flows directly into the fuel tank. This reduces the time to purge all vapor from the system during start up. The LPG bypass solenoid has a built in over flow valve that will reduce the flow of LPG if the pressure difference between the inlet and outlet of the valve is greater than the calibrated amount. There is also a manual shut-off valve integrated into the LPG bypass solenoid.

LPG Pressure and Temperature Sensor

The combination LPG pressure and temperature sensor is located at the back of the right hand side fuel rail. The LPG control module provides a reference voltage and ground to the sensor and receives the fuel pressure and temperature signals from the combination sensor. The signals are used to calculate the amount of purge time required for start up.

LPG Control Module

The LPG control module is mounted under the center of the dash above the engine cover. It controls the amount of time the wait to start indicator is illuminated and the amount of time the LPG bypass solenoid valve is energized. The LPG control module provides a 5 v reference voltage and ground to the fuel/temperature sensor. The return signals from the sensor are used to determine if the system needs to be purged and for how long the system needs to be purged. The LPG control module also controls both the wait to start indicator relay, bypass relay, and evaporative emissions vacuum pump. The LPG control module monitors the signal and control circuits for proper operation. If a fault is detected the LPG control module will command the wait to start indicator to flash for 0.5 second for a total equal to the fault number. There will be a 3 second pause between flashes or a 6 second pause if multiple faults are present.

The fuel injector rails are built of billet aluminum for minimum heat transfer. Fuel is supplied to the injectors through dedicated supply passages and the return fuel is returned to the tank through separate return passages.

Each fuel injector has a supply passage and a return passage. The passage in the injector from the supply section to the return section is restricted by a cooling bushing. As liquid propane passes through the cooling bushing, a pressure reduction takes place, which causes the propane to vaporize and effectively cools the area around the supply section. This is called a refrigeration cycle and aids in maintaining the fuel in a liquid state for all driving conditions, regardless of the outside temperature. The design of the injector compensates for changes in the fuel pressure so a specific fuel pressure is not required.

Starting Mode

When the ignition is first turned ON, the ECM supplies voltage to the LPG control module for 30 seconds. While this voltage is being received, the fuel pump relay supplies battery voltage to the primary fuel pump and LPG cut-off solenoid to allow liquid propane to circulate through the entire system. This is done to evacuate all propane vapor from the fuel system. The ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode

Run Mode

Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.

Acceleration Mode

Deceleration Mode

Battery Voltage Correction Mode

When the battery voltage is low, the ECM compensates for the weak spark delivered by the ignition system in the following ways

Increasing the amount of fuel delivered
Increasing the idle RPM
Increasing the ignition dwell time

Fuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability

The ignition is OFF. This prevents engine run-on.
The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
The engine speed is too high, above red line.
The vehicle speed is too high, above rated tire speed.
During an extended, high speed, closed throttle coast down-This reduces emissions and increases engine braking.
During extended deceleration, in order to prevent damage to the catalytic converters

The Fuel System is an electronic returnless on-demand design. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

An electric turbine style fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pump and sender assembly contains a reverse flow check valve. The check valve maintains fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

E85 Flex Fuel Description

E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.

The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. The fuel alcohol content percentage value can be read on a scan tool.

When an E85 compatible vehicle is built, an ECM or PCM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10 percent or less ethanol content.

A minimum of 11 liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition OFF in order to have the re-fueling event recognized, however local safety regulations should be followed.

After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop operation.

Switching Between Gasoline and E85

No special precautions need to be taken when switching back and forth between gasoline and E85 other than re-fueling events must be 11 liters (3 gallons) or greater, and the vehicle must remain in closed loop long enough, usually by the time the engine has maintained full operating temperature, to calculate the composition of the new blend in the tank.

Fuel Pump Flow Control Module (FPCM)

The fuel pump flow control module (FPCM) is a serviceable GMLAN module. The FPCM receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The FPCM sends a 25 KHZ PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 15 amps. A liquid fuel pressure sensor provides fuel pressure feedback to the FPCM.

Electronic Returnless Fuel System (ERFS)

The electronic returnless fuel system is a microprocessor controlled fuel delivery system which transports fuel from the tank to the fuel rails. It functions as an electronic replacement for a traditional, mechanical fuel pressure regulator. A pressure relief regulator valve within the fuel tank provides an added measure of over pressure protection. Desired fuel pressure is commanded by the engine control module (ECM), and transmitted to the FPCM via a GMLAN serial data message. A liquid fuel pressure sensor provides the feedback the FPCM requires for Closed Loop fuel pressure control.

Liquid Fuel Pressure Sensor - With FPCM

The fuel pressure sensor is a serviceable 5-volt, 3-pin device. It is located on the fuel feed line forward of the fuel tank, and receives power and ground from the fuel pump flow control module (FPCM) through a vehicle wiring harness. The sensor provides a fuel pressure signal to the FPCM, which is used to provide Closed Loop fuel pressure control.

The fuel tanks store the fuel supply. The front fuel tank is located on the left side of the vehicle. On dual-tank applications, the secondary fuel tank is located in the rear of the vehicle above the spare tire. The fuel tanks are each held in place by 2 metal straps that attach to the frame. The fuel tanks are molded from high density polyethylene.

Scheme 199

Scheme 199: Fuel Fill Pipe

The fuel fill pipe has a built-in restrictor in order to prevent refueling with leaded fuel. When refueling dual tank applications, fuel is dispensed to both the front and rear fuel tanks at the same time. Once the fill vent is obstructed, fuel backs up the fill pipe and trips the dispensing nozzle.

Scheme 200

The front fuel tank vent runs into the rear tank to the top of the filler pipe assembly, which in turn vents to atmosphere. The fuel tank vent valves are connected and route to the canister to collect hydrocarbon emissions during operation of the vehicle.

Scheme 201

Scheme 201: Fuel Filler Cap

The fuel fill pipe has a tethered fuel filler cap. A torque-limiting device prevents the cap from being over tightened. To install the cap, turn the cap clockwise until you hear clicks. This indicates that the cap is correctly torqued and fully seated. A built-in device indicates that the fuel filler cap is fully seated. A fuel filler cap that is not fully seated may cause a malfunction in the emission system.

Scheme 202

Scheme 202: Fuel Tank Fuel Pump Module Assembly

The front fuel tank fuel pump module on dual tank applications consists of the following major components

The fuel level sensor
The fuel strainer
The fuel filter
The pressure relief regulator valve

Scheme 203

The rear fuel tank fuel pump module on dual tank applications consists of the following major components

The fuel level sensor (4)
The FTP sensor (1)
The rear fuel pump (2)

The fuel tank fuel pump module assembly on single tank applications consists of the following major components

The fuel level sensor
The fuel tank pressure (FTP) sensor
The fuel strainer
The fuel filter
The pressure relief regulator valve

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor cord. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor, which changes resistance in correspondence to the amount of fuel in the fuel tank. The engine control module (ECM) sends the fuel level information via the class 2 circuit to the instrument panel (I/P) cluster. This information is used for the I/P fuel gauge and the low fuel warning indicator, if applicable. The ECM also monitors the fuel level input for various diagnostics.

The fuel pump is mounted in the fuel tank fuel pump module assembly reservoir. The fuel pump is an electric high pressure pump. Fuel is pumped to the fuel injection system at a pressure that is based on feedback from the fuel pressure sensor. The fuel pump delivers a constant flow of fuel to the engine during low fuel conditions and aggressive vehicle maneuvers. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

Pressure Relief Regulator Valve

The pressure relief regulator valve replaces the typical fuel pressure regulator used on a mechanical returnless fuel system. The pressure relief regulator valve is closed during normal vehicle operation. The pressure relief regulator vale is used to vent pressure during hot soaks and also functions as a fuel pressure regulator in the event of the fuel pump flow control module defaulting to 100 % pulse width modulation (PWM) of the fuel pump. Due to variation in fuel system pressures, the opening pressure for the pressure relief regulator vale is set higher than the pressure that is used on a mechanical returnless fuel system pressure regulator.

Fuel Strainer

The fuel strainer attaches to the lower end of the fuel tank fuel pump module. The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment.

The fuel filter is contained in the fuel tank fuel pump module assembly inside the fuel tank. The paper filter element of the fuel filter traps particles in the fuel that may damage the fuel injection system. The fuel filter housing is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no service interval for fuel filter replacement.

Nylon Fuel Pipes

WARNING

Refer to Fuel and Evaporative Emission Pipe Warning .

Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. Heat resistant rubber hose or corrugated plastic conduit protects the sections of the pipes that are exposed to chafing, to high temperatures, or to vibration.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if nylon fuel pipes are forced into sharp bends, the pipes kink and restrict the fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working on a vehicle with nylon fuel pipes.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female connector, provide the fuel seal. Integral locking tabs inside the female connector hold the fittings together.

The On-Board Refueling Vapor Recovery System (ORVR) is an on-board vehicle system designed to recover fuel vapors during the vehicle refueling operation. The flow of liquid fuel down the fuel filler pipe provides a liquid seal which prevents vapor from leaving the fuel filler pipe. An evaporative emission (EVAP) pipe transports the fuel vapor to the EVAP canister for use by the engine.

Fuel Pipe O-Rings

O-rings seal the threaded connections in the fuel system. Fuel system O-ring seals are made of special material. Service the O-ring seals with the correct service part.

Fuel Rail Assembly

The fuel rail assembly attaches to the engine intake manifold. The fuel rail assembly performs the following functions

Positions the injectors (3) in the intake manifold
Distributes fuel evenly to the injectors

Fuel Injectors

The fuel injector assembly is a solenoid device controlled by the engine control module (ECM) that meters pressurized fuel to a single engine cylinder. The ECM energizes the injector solenoid to open a normally closed ball valve. This allows the fuel to flow into the top of the injector, past the ball valve, and through a director plate at the injector outlet. The director plate has machined holes that control the fuel flow, generating a spray of finely atomized fuel at the injector tip. Fuel from the injector tip is directed at the intake valve, causing the fuel to become further atomized and vaporized before entering the combustion chamber. This fine atomization improves fuel economy and emissions.

Starting Mode

When the ignition is first turned ON, the ECM supplies voltage to the FPCM for 2 seconds. While this voltage is being received, the FPCM closes the ground switch of the fuel pump, and also supplies a varying voltage to the fuel tank fuel pump module in order to maintain the desired fuel rail pressure. The ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode

Run Mode

Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.

Acceleration Mode

Deceleration Mode

Battery Voltage Correction Mode

When the battery voltage is low, the ECM compensates for the weak spark delivered by the ignition system in the following ways

Increasing the amount of fuel delivered
Increasing the idle RPM
Increasing the ignition dwell time

Fuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability

The ignition is OFF. This prevents engine run-on.
The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
The engine speed is too high, above red line.
The vehicle speed is too high, above rated tire speed.
During an extended, high speed, closed throttle coast down-This reduces emissions and increases engine braking.
During extended deceleration, in order to prevent damage to the catalytic converters

EVAP System Operation (LC8, FHZ)

The evaporative emission (EVAP) control system on a compressed natural gas (CNG) fueled vehicle has been disabled. Many of the components are removed with the exception of the EVAP purge solenoid valve. However, the EVAP purge solenoid valve does not purge fuel vapors. The vapor line port is capped. The EVAP purge solenoid valve is utilized with the ECM fuel calibration for CNG control. There are no DTCs associated with the EVAP purge solenoid valve. Scan tool support for EVAP control system has been removed as well.

Scheme 204

Scheme 204: Typical Evaporative Emission (EVAP) System Hose Routing Diagram

Callout	Component Name
1	Evaporative Emissions (EVAP) Purge Solenoid Valve
2	EVAP Canister
3	EVAP Vapor Tube
4	Vapor Recirculation Tube
5	Fuel Tank Pressure Sensor
6	Fuel Filler Cap (Some Vehicles May Have A Capless Design)
7	Fuel Fill Pipe Inlet Check Valve
8	Fuel Tank
9	EVAP Canister Vent Solenoid Valve
10	Vent hose
11	EVAP Purge Tube
12	Purge Tube Check Valve, Turbo-Charged Applications Only
13	EVAP Canister Purge Tube Connector

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the EVAP vapor tube, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent hose and EVAP canister vent solenoid valve to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the engine control module (ECM) will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister. With the normally open EVAP canister vent solenoid valve OFF, fresh air is drawn through the vent solenoid valve and the vent hose to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge tube and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking or restricted.

Purge Solenoid Valve Leak Test

If the evaporative emission (EVAP) purge solenoid valve does not seal properly fuel vapors could enter the engine at an undesired time, causing driveability concerns. The ECM tests for this by commanding the EVAP purge solenoid valve OFF and the canister vent solenoid valve ON which seals the system. With the engine running, the ECM then monitors the fuel tank pressure sensor for an increase in vacuum. The ECM will log a fault if a vacuum develops in the tank under these test conditions.

Large Leak Test

This diagnostic creates a vacuum condition in the EVAP system. When the enabling criteria has been met, the control module commands the normally open EVAP canister vent solenoid valve closed and the EVAP purge solenoid valve open, creating a vacuum in the EVAP system. The ECM then monitors the fuel tank pressure sensor voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. Failure to achieve the expected level of vacuum indicates the presence of a large leak in the EVAP system or a restriction in the purge path. The ECM will log a fault if it detects a weaker than expected vacuum level under these test conditions.

Canister Vent Restriction Test

If the evaporative emission (EVAP) vent system is restricted, fuel vapors will not be properly purged from the EVAP canister. The control module tests this by commanding the EVAP purge solenoid valve ON while commanding the EVAP canister vent solenoid valve OFF, and then monitoring the fuel tank pressure sensor for an increase in vacuum. If the vacuum increases more than the expected amount, in a set amount of time, a fault will be logged by the ECM.

Small Leak Test

The engine off natural vacuum diagnostic is the small-leak detection diagnostic for the evaporative emission (EVAP) system. The engine off natural vacuum diagnostic monitors the EVAP system pressure with the ignition OFF. Because of this, it may be normal for the control module to remain active for up to 40 minutes after the ignition is turned OFF. This is important to remember when performing a parasitic draw test on vehicles equipped with engine off natural vacuum.

When the vehicle is driven, the temperature rises in the tank due to heat transfer from the exhaust system. After the vehicle is parked, the temperature in the tank continues to rise for a period of time, then starts to drop. The engine off natural vacuum diagnostic relies on this temperature change, and the corresponding pressure change in a sealed system, to determine if an EVAP system leak is present.

The engine off natural vacuum diagnostic is designed to detect leaks as small as 0.51 mm (0.020 in).

EVAP System Components

The evaporative emission (EVAP) system consists of the following components

EVAP Canister Purge Solenoid Valve

The EVAP canister purge solenoid valve controls the flow of vapors from the EVAP system to the intake manifold. The purge solenoid valve opens when commanded ON by the control module. This normally closed valve is pulse width modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The valve will also be opened during some portions of the EVAP testing when the engine is running, allowing engine vacuum to enter the EVAP system.

Purge Tube Check Valve

Turbocharged vehicles have a check valve in the purge tube between the EVAP purge solenoid valve and the EVAP canister to prevent pressurization of the EVAP system under boost conditions. Note that the presence of this one-way check valve prevents pressure testing the EVAP system for leaks at the EVAP canister purge tube connector.

EVAP Canister

The canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapor is stored in the canister until the control module determines that the vapor can be consumed in the normal combustion process.

Vapor Recirculation Tube

A vapor path between the fuel fill pipe and the vapor tube to the carbon canister is necessary for Vehicle Onboard Diagnostics to fully diagnose the EVAP system. It also accommodates service diagnostic procedures by allowing the entire EVAP system to be diagnosed from either end of the system.

Fuel Tank Pressure Sensor

The fuel tank pressure sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. The control module provides a 5 V reference and a ground to the fuel tank pressure sensor. Depending on the vehicle, the sensor can be located in the vapor space on top of the fuel tank, in the vapor tube between the canister and the tank, or on the EVAP canister. The fuel tank pressure sensor provides a signal voltage back to the control module that can vary between 0.1-4.9 V. A high fuel tank pressure sensor voltage indicates a low fuel tank pressure or vacuum. A low fuel tank pressure sensor voltage indicates a high fuel tank pressure.

Fuel Fill Pipe Check Valve

The check valve on the fuel fill pipe is there to prevent spit-back during refueling.

EVAP Canister Vent Solenoid Valve

The EVAP vent solenoid valve controls fresh airflow into the EVAP canister. The valve is normally open. The canister vent solenoid valve is closed only during EVAP system tests performed by the ECM.

Fuel Fill Cap

The fuel fill cap is equipped with a seal and a vacuum relief valve.

Evaporative Emission Control System Description (LC8\ K07\ UFM)

This description deals with the 3 tank (UFM) liquid propane gas (LPG) - (K07) system.

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. During engine Off mode a vacuum pump pulls fuel vapor from the engine and stores them in the EVAP canister. At an appropriate time, the engine control module (ECM) will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister.

Fresh air is drawn through a hose spliced into the PCV system then to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge tube and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion.

The purge solenoid valve, controlled by the ECM, will purge fuel vapors during engine run mode. This is separate from and not to be confused with the purge mode described under Fuel System Description (LC8,K07,UFM), Fuel System Overview.

Note. The conventional EVAP control system on this LPG fueled vehicle has been disabled. Many of the components are removed with the exception of the EVAP purge solenoid valve. All the associated EVAP DCT's have also been turned off and therefore there is no scan tool support for this LPG system.

Note. The liquid propane injection system utilizes a unique EVAP sub-system to maintain compliant levels of evaporative emissions. The system consists of the addition of vapor lines and a vacuum pump controlled by the LPG Control Module.

The EVAP system consists of the following components

EVAP Purge Solenoid Valve

The EVAP purge solenoid valve controls the flow of vapors from the EVAP sub-system to the intake manifold. The purge solenoid valve opens when commanded ON by the ECM. This normally closed valve is pulse width modulated (PWM) by the ECM to precisely control the flow of fuel vapor to the engine.

EVAP Canister

The canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapor is stored in the canister until the ECM determines that the vapor can be consumed in the normal combustion process.

Vacuum Pump

The vacuum pump is housed in a protective box and mounted on a bracket next to the EVAP canister. Additional vapor lines are spliced into the purge and PCV lines to complete this sub-system. When the engine is off, the vacuum pump moves fuel rich vapor from the engine to the EVAP canister for storage. The system operates during this engine off mode when the following criteria is met.

Ignition Off for 20 min
Battery voltage greater than 10.8 V
Pump On for 2 min
Pump Off for up to 20 min
Steps 3 and 4 repeat for up to 110 h or battery voltage less than 10.8 V

This will reset when the ignition key is cycled on.

Electronic Ignition System Operation

The electronic ignition system produces and controls the high energy secondary spark. This spark ignites the compressed air/fuel mixture at precisely the correct time, providing optimal performance, fuel economy, and control of exhaust emissions. The engine control module (ECM) primarily collects information from the crankshaft position and camshaft position sensors to control the sequence, dwell, and timing of the spark.

Crankshaft Position Sensor

The crankshaft position sensor is an internally magnetic biased digital output integrated circuit sensing device. The sensor detects magnetic flux changes of the teeth and slots of the reluctor wheel on the crankshaft. The reluctor wheel is spaced at 60-tooth spacing, with two missing teeth for the reference gap. The reference gap is used to identify the crankshaft position at each start-up. The crankshaft position sensor produces an ON/OFF DC voltage of varying frequency, with 58 output pulses per crankshaft revolution. The crankshaft position sensor sends a digital signal to the ECM as each tooth on the reluctor wheel rotates past the crankshaft position sensor. The ECM uses each crankshaft position signal pulse to determine crankshaft speed position. This information is then used to determine the optimum ignition and injection points of the engine. The ECM also uses crankshaft position sensor output information to determine the camshaft relative position to the crankshaft, to control camshaft phasing, and to detect cylinder misfire.

The ECM also has a dedicated replicated crankshaft position sensor signal output circuit that may be used as an input signal to other modules for monitoring engine RPM.

Camshaft Position Sensor

The camshaft position sensor detects magnetic flux changes between the four narrow and wide tooth slots on the reluctor wheel. The camshaft position sensor provides a digital ON/OFF DC voltage of varying frequency per each camshaft revolution. The ECM will recognize the narrow and wide tooth patterns to identify camshaft position, or which cylinder is in compression and which is in exhaust. The information is then used to determine the correct time and sequence for fuel injection and ignition spark events.

Knock Sensor

The knock sensor system enables the engine control module (ECM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation, also known as spark knock. The knock sensor system uses one or two flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the knock sensor detects. The ECM receives the knock sensor signal through two isolated signal circuits for each knock sensor.

The control module learns a minimum noise level, or background noise, at idle from the knock sensor and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal knock sensor signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal knock sensor signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses knock sensor signal information when each cylinder is near top dead center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel.

If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal knock sensor signal will stay outside of the noise channel or will not be present. knock sensor diagnostics are calibrated to detect faults with the knock sensor circuitry inside the control module, the knock sensor wiring, or the knock sensor voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise.

Ignition Coils

Each ignition coil has an ignition 1 voltage feed and a ground circuit. The engine control module (ECM) supplies a low reference and an ignition control circuit. Each ignition coil contains a solid state driver module. The ECM will command the ignition control circuit ON, which allows the current to flow through the primary coil windings. When the ECM commands the ignition control circuit OFF, this will interrupt current flow through the primary coil windings. The magnetic field created by the primary coil windings will collapse across the secondary coil windings, which induces a high voltage across the spark plug electrodes.

Engine Misfire Detection

The crankshaft position sensor is used to determine when an engine misfire is occurring. The camshaft position sensor is used to determine which cylinder is misfiring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM is able to detect individual misfire events. For accurate detection of engine misfire, the ECM must distinguish between crankshaft deceleration caused by actual misfire and deceleration caused by rough road conditions. The antilock brake system (ABS) can detect if the vehicle is on a rough road based on wheel acceleration/deceleration data supplied by the wheel speed sensors. If the ABS detects rough road above a predetermined threshold, this information is sent to the ECM. The ECM uses the rough road information when calculating engine misfire. Under certain driving conditions, a misfire rate can be high enough to cause the 3-way catalytic converter to overheat damaging the converter. The malfunction indicator lamp (MIL) will flash ON and OFF when converter overheating, damaging conditions are present.

Fast Idle

Fast Idle (UF3) is available on heavy duty engines equipped with cruise control. The purpose of fast idle is to increase engine idle speed. The system is controlled through the steering wheel mounted cruise control switches. Upon activation a signal is sent through the body control module (BCM) to the engine control module (ECM) commanding an increase in engine speed.

The instrument panel will indicate the fast idle system is active by displaying a message across the driver information center (DIC).

Fast Idle Enable and Disable

To enable the fast idle system, perform the following procedure

Engine running.
Park brake set.
Transmission shifter in P (park) or N (neutral).
Press and release the cruise control ON/OFF button.
Press and release the cruise control SET button.

When the procedure is followed the engine idle speed will increase to approximately 1,200 RPM.

The manual fast idle system will be disabled if any of the following procedures are performed

Brake applied
Cruise control CANCEL, ON/OFF, or SET buttons depressed
Park brake released
Accelerator pedal depressed more than 25%
Clutch applied
Ignition switch turned to the LOCK/OFF position

Engine Controls/fuel - 4.8l (l20), 5.3l (Lmf), or 6.0l (l96 lc8) - Description and Operation Chevrolet Express G3500

Engine Control Module Description

ECM Function

EEPROM

Data Link Connector (DLC)

Malfunction Indicator Lamp (MIL)

ECM Service Precautions

Emissions Diagnosis For State I/M Programs

Aftermarket (Add-On) Electrical And Vacuum Equipment

Electrostatic Discharge (ESD) Damage

Emissions Control Information Label

Scheme 197

Modes Of Operation

Camshaft Position (CMP) Actuator System

CMP Actuator System Operation

Fuel System Overview

Compressed Natural Gas (CNG) Fuel Tanks

CNG High Pressure Lock-Off (HPL) Solenoid Valves

CNG Tank Pressure Relief Device (PRD)

CNG Fill Receptacle and Lines

CNG Fuel Lines

CNG 1/4 Turn Isolation Valve

Fuel Tank Pressure (FTP) Sensor

CNG Fuel Filter

Compressed Natural Gas (CNG) Control Module

High Pressure Regulator (HPR)

CNG Fuel Injectors

On-Board Refueling Vapor Recovery System (ORVR)

Scheme 198

Fuel Metering Modes of Operation

Fuel Trim

Fuel Tanks

Overfilling Prevention Device

Over Flow Valves

Pressure Relief Valve

Fill Filter

Fill Valve

Fuel Pump Filter

Fuel Pump

Fuel Transfer Pump

Fuel Lines

Fuel Level Sensors

Liquid Propane Delivery Module

Liquid Propane Control Module

Fuel Injector Rails

Fuel Injector

Fuel Filter

Fuel Level Sensor

LPG Cut-Off Solenoid

LPG Bypass Solenoid

LPG Pressure and Temperature Sensor

LPG Control Module

E85 Flex Fuel Description

Switching Between Gasoline and E85

Fuel Pump Flow Control Module (FPCM)

Electronic Returnless Fuel System (ERFS)

Liquid Fuel Pressure Sensor - With FPCM

Scheme 199

Scheme 200

Scheme 201

Scheme 202

Scheme 203

Pressure Relief Regulator Valve

Fuel Strainer

Nylon Fuel Pipes

Quick-Connect Fittings

Fuel Pipe O-Rings

Fuel Rail Assembly

Fuel Injectors

EVAP System Operation (LC8, FHZ)

Scheme 204

EVAP System Operation

Purge Solenoid Valve Leak Test

Large Leak Test

Canister Vent Restriction Test

Small Leak Test

EVAP System Components

Evaporative Emission Control System Description (LC8\ K07\ UFM)

Electronic Ignition System Operation

Crankshaft Position Sensor